1. Field of the Invention
The present invention relates to a pressure measuring method. In particular, it relates to a pressure measuring method wherein the pressure measurement is performed by pressing a pressure-sensitive recording sheet interposed between the parts to be measured through a sheet meterial having regular embossed patterns.
2. Description of the Prior Art
Recently, it has become of interest to mechanically measure various line pressures, face pressures, etc., such as the clamping pressure of bolts for general machinery and tools; the pressing condition of motor brake gears, the molding pressure and mold clamping pressure on molding thermoplastic resins or thermosetting resins; the contact pressure between a resin in a mold and the wall of the mold; the molding pressure in a mold; the contact face pressure of springs; the clamping face pressure in connected portions of fuel carburettors, fuel pipes, fuel tanks, etc.; the collision pressure between the human body and instruments or implements at car crash; the line pressure and face pressure of a rubber roll and a plastic roll; checking of the effective limit or the effective state of gasket seals; the oil pressure in brake gears; the contact condition of gear teeth; the contact face pressure between solid materials; the clamping pressure of bolts; checking the contact condition of a cock in a cock valve; checking of the contact condition between curved surfaces; checking of the contact condition of rolling rolls for steel in operation; the pressure distribution of the sole of a human foot on a floor; the pressure distribution between a human body and a chair or sofa; and the like. In spite of this, a method capable of measuring pressure in a simple manner has not yet been developed or if any, the method is very complicated.
That is to say, known conventional methods of measuring pressures such as face pressures and line pressures, are, for instance, a method wherein a strain gauge utilizing a relation between stress and strain is employed, a method wherein a load meter is used, and method wherein a pressure-sensitive paint (strain-sensitive lacquer) is used. However, these conventional methods have the following disadvantages.
That is, in using a strain gauge, e.g., described in detail in, for instance, J. Yarnell; Strain Gauge published by Corona Sha, for the measurement of face pressures, line pressures, etc., not only large pieces of equipment such as an amplifier, a detector, a recorder, etc., are required but also highly skilled techniques and complicated calculations of the strength of materials are required for operating these equipment. Furthermore, the materials to be measured in the method must have flat surfaces due to the characteristics of the method.
Also, in the method using a pressure-sensitive paint (strain-sensitive lacquer), unevenness in coating tends to occur, problems due to the adhesivity of the pressure-sensitive paint exist, and further the method is complicated.
In using a load meter for measuring pressures, it is impossible to reduce the size of the equipment, which results in use of a load meter being inappropriate for the measurement of pressures such as face pressure, line pressure, etc.
Still further, a method is known wherein a pressure-sensitive laminate is used as disclosed in U.S. Pat. No. 3,647,504. In this method, a mono-ply type pressure-sensitive recording paper carrying microcapsules of two or more different kinds each having a different wall thickness and each containing a marking liquid with a different color is used. Thus, only a specific kind of microcapsules is ruptured in response to each specific pressure to release the colored marking liquid in those microcapsules and hence the extent of the pressure applied can be detected by observing the color tone formed.
However, although the method described above can be used to determine roughly the extent of the pressure applied, it is difficult, with such a method, to detect precisely or correctly the value of the pressure applied.
To overcome the disadvantages in these conventional techniques, a method has been used wherein a pressure-sensitive sheet is brought into contact with a part where pressure is to be measured and a pressure is applied to the recording sheet through the part to form color, whereby the value of the pressure applied is detected from the change in optical density of the colored marks or images formed on the pressure-sensitive recording sheet. In this method, the coloring of the pressure-sensitive recording sheet can be performed by the contact of a color former and a color developer under pressure. The advantage of this method is that pressures such as face pressure, line pressure, etc., at the portions to be measured can be measured without need of large pieces of equipment, highly skilled operation techniques, and complicated calculations.
However, the support of the recording sheet used in this method has generally a flat or irregular and uneven surface and hence the colored marks or images formed by pressing the recording sheet show an uneven color density, which makes it impossible to detect precisely the value of the pressure applied.
It is believed that when a support having an irregular and uneven surface is used, the irregular and uneven patterns are transferred to cause a color density unevenness but it has not yet been clarified why such a color density unevenness occurs in using a support having a flat surface. The reason is assumed to be as follows.
The first reason is believed to originate in the properties of the microcapsules which contribute to coloring. That is, it is believed that since the pressure is directly applied to all the microcapsules containing a color former, the rupture of the microcapsules is greatly influenced by the unevenness in particle size of the microcapsules or in the thickness of the wall of the microcapsules; which results in an irregular localized unevenness in optical density of recorded marks or images occurring.
The second reason is believed to originate in the influence of gases such as air, etc., present at the portions to be measured. That is, it is believed that when a pressure is applied to the pressure-sensitive recording sheet having a flat surface at the part to be measured, a gas present at the interface between the recording sheet and the surface of a material in contact with the recording sheet is confined locally, which causes an unevenness in pressure applied to the pressure-sensitive recording sheet and results subsequently in the irregular localized unevenness in optical density of the colored marks or images.